1. Field of the Invention
This invention relates to multiple-battery electric systems, and more particularly relates to electric equipment, such as an electric vehicle, powered by a redundant array of batteries.
2. Description of the Related Art
Electric equipment, such as an electric vehicle (“EV”), utilizes chemical energy stored in rechargeable batteries which is converted to electricity. EVs use electric motors instead of, or in addition to, internal combustion engines. In the latter case, the EV is referred to as a hybrid electric vehicle (“HEV”). At the heart of an EV, there are three main components: batteries, electric motor controller, and electric motor. Batteries supply power to the electric motor controller, which controls the amount of voltage and current supplied to the electric motor based on the position of the accelerator pedal. Batteries used in EVs vary in type, number, voltage and placement. Operating voltage can be 360 volts (or higher). With the use of 12-volt batteries, for instance, 30 batteries (or more) connected in series are required to obtain such voltage.
Nowadays more and more EVs are traveling on the U.S. roads and highways. Batteries used to power the EVs are rapidly becoming very important components of the vehicles. Current battery technology is adequate for EVs with a range, for example, of 250 miles, but the batteries are still rather expensive and require elaborate safety mechanisms. One type of batteries known as lithium-ion batteries, being widely used in laptops, cell phones, and other mobile devices, fall in that category. In the wake of recent massive recalls of Sony lithium-ion batteries used in millions of laptop computers because of incidents of battery overheating or bursting into flames, many industry experts are paying tremendous attention to the safety enhancements of these batteries, as well as other types of batteries.
Because of the small form factor, environmentally friendliness, and desired energy density achievability, lithium-ion cells, in particular, are increasing in popularity among some EV manufacturers as well, when selecting batteries for their end products. Some battery packs they use are capable of delivering as much as 200 kilowatts of electric power. For that kind of capacity, the manufacturers consider safety as a primary criterion in the battery pack's design and architecture. Packaging and cooling system designs are also important considerations.
In addition to cell-level safety protection, those manufacturers provide multiple battery pack level safety features. Besides cell fuses, a pack that may include a number of battery modules has module fuses, each guarding against a short circuit across the complete module. Microprocessors, logic circuitry and sensors are used to continually monitor voltages, currents and temperatures within the pack. During normal vehicle operation, the battery logic board communicates with the vehicle to initiate battery cooling, report state of charge, and signal battery faults. Additionally, to enhance battery safety, whenever at least one of the fault conditions, such as over current, short circuit, cell and pack over-voltage and over temperature, occurs, with a certain design, the battery cells are disconnected from the system by turning off two back-to-back protection MOSFETs that are connected in series with the battery pack. Manufacturers claim that a fundamental element of the vehicle and battery pack safety design is the ability to electrically disconnect the high voltage of the pack from the rest of the vehicle (by controlling high voltage contactors, for example) if any number of adverse conditions are detected.
If the EV is moving when a serious cell failure occurs, the numerous built-in electronic sensors will detect the failure and will disconnect the high voltage from the vehicle. Unfortunately, this will bring the vehicle to a stop, with all the high voltage and energy contained within the battery pack. Following a serious battery failure, the vehicle will be inoperable until the battery pack is serviced. This can happen anywhere on the road, causing the vehicle driver to be stranded, possibly in the middle of nowhere. That can place him/her in an unsafe situation.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that enable the EV to keep moving until the driver determines it is safe to stop the vehicle for a service action on the faulty battery. Beneficially, such an apparatus, system, and method would enhance the value of the EV.